Found in a chest behind the Forgotten Door in Majula's Deep Pit. It can be reached by navigating the Deep Pit using fall-damage reducing equipment, such as the Silvercat Ring (it's safer to remove all other equipment before jumping). The Deep Pit can also be navigated by using a ladder built by Laddersmith Gilligan, after he arrives in Majula. He will create the ladder for 12,000 souls. After climbing down the ladder, proceed to climb up the metal ladder to the Forgotten Door.